Heat absorbing temperature control devices and method

ABSTRACT

The increase of temperature in heat sensitive devices during heat generating conditions is prevented through the absorption of heat, by providing Aldehyde in an amount sufficient to effect the required heat absorption. Where the heat generating conditions are generated by a heat generator, separate and distinct from the heat sensitive device, the Aldehyde is supported in a position between the heat sensitive device and the heat generator. Where the heat sensitive device is itself the heat generator, the Aldehyde is contacted to the heat sensitive device either directly or indirectly.

RELATED APPLICATIONS

[0001] This application is a divisional of U.S. patent application Ser.No. 09/558,949 filed on Apr. 26, 2000, which in turn was aContinuation-In-Part of U.S. patent application Ser. No. 08/709,516filed on Sep. 6, 1996, which in turn claims the benefit of U.S.Provisional Application Ser. No. 60/003,387 filed on Sep. 7, 1995.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to heat absorbing devices and amethod for constructing same. Said heat absorbing devices have heatabsorbing chemicals, i.e. endotherms, which use their respective heatsof reaction to cool and maintain and control the temperature and heat ofheat sensitive devices. These endotherms comprise certain acids andtheir salts, certain bases and their salts, and certain organiccompounds, which have never before been used in the manner described,disclosed and claimed below.

[0003] Often, active cooling of such electronic components, particularlydelicate TR modules, Impatt diodes, data recorders, containers forchemicals and munitions, batteries and the like, is not feasible; andeven when it is feasible, it requires continuous high energy cooling,which taxes other ancillary engineering systems typical in missiles,aircrafts, railroads, trucks, automobiles, guns, nuclear reactorsystems, related combat systems, as well as commercial systems andtechnology.

[0004] The heat sinks of the prior art generally employ phase changematerial compositions (PCMs) for the absorption and dissipation of heat.The conventional PCM materials are largely solid or fluidic in nature,i.e. liquids, quasi-liquids, or solids such as waxes or other meltablecompositions. However, these conventional PCMs have proven to sufferfrom many technical problems, as well as problems in their use andapplication. These problems include relatively low latent heats offusion, the inability to control the shape and form of such fluid PCMmaterials, as well as the unevenness of heating and cooling. Otherproblems include the need to provide a containment housing and thestress placed on the housing, resulting in frequent rupture and spillageof the PCM; the hazard to life and property due to PCMs' high heatcontent and flammability; and lastly, the uneven cooling hysteresis.

[0005] In addition, the known PCMs can spill hot fluids onto a human'sskin, resulting in serious third degree burns due to the sticky contactnature of many hot wax and polymer or plastic phase change materials(PCMs) and the high heat and sticky adherence to the skin. Rupturednon-Composite Fabric Endothermic Material (CFEM) or liquified bulk PCMdisks spill their content and cause flash fires, which spread as the PCMpours out during heating in ovens and wax-filled disks are prone tofires, which can spread and flow out of stoves.

[0006] Applicant has addressed some of these and other PCM problems inhis, U.S. Pat. No. 4,446,916. Applicant has disclosed what he calls acomposite fabric endothermic material (CFEM), providing devicesespecially suitable as heat sinks for aerospace and military use. Thepatented CFEM provides an improved heat sink that absorbs heat at themelting temperatures of a compound embedded within a fibrous mesh ormatrix. The CFEM preferably comprises a phase change material, which isheld by capillary action and chemical adhesion to the fibers of thematrix. As a result a greatly increased surface area for heat transferis obtained; thus providing for controlled melting and thermaldissipation of the fusion cooling agent.

[0007] Applicant has also addressed some of the PCM problems in hispending U.S. patent application Ser. No. 08/183,199, now U.S. Pat. No.5,709,915, the disclosure and contents of which are incorporated hereinas if more fully set forth. Such application addresses the need for animproved recyclable endothermic/exothermic thermal storage method foruse in many commercial and civilian applications, particularly for food,home and commercial packaging operations. In this application, improvedCFEMs are disclosed, capable of being employed in a variety ofcommercial applications such as in the food industry where a need hasarisen for heat retaining or heat insulating containers, packages andthermal storage devices.

[0008] However, the active agents suggested in Applicant's pending U.S.patent application Ser. No. 08/183,199, now U.S. Pat. No. 5,709,914 arenot useful in the present inventive heat absorbing devices, as they areconcomitantly both endotherms and exotherms. i.e. first, they absorbheat and then they give off heat to the item in connection with whichthey are being used, for the purpose of maintaining it warm.

[0009] While they can accomplish some protection from high temperaturesthrough the physical phenomenon of the absorption of their latent heatof fusion, wherein the appropriate crystalline substance absorbs aquantity of heat to melt without a temperature rise to its surroundings,they are totally unsuitable for applications relating to the absoluteprotection of heat sensitive devices from high heat. After all, the heatthey have absorbed, they must release. In other words, not only do theyabsorb heat but they also release heat, particularly when confined in aclosed environment.

[0010] Another problem with the active agents of Applicant's, U.S.pending patent application Ser. No. 08/183,199, now U.S. Pat. No.5,709,914 and the prior art PCMs is that they are not capable ofabsorbing more than 200 cal/gm. Thus, they can remove heat for only ashort period of time relative to mass and only at temperatures notexceeding 326° F. Consequently, they are not effective for applicationsrequiring cooling at very high temperatures and for long periods of timeas would be needed, for example, in airplane and railroad crashrecorders, missile electronics, spacecraft devices, power supplies, datarecorders employed as aircraft and railroad components and combatdevices, and in commercial uses such as oven sensors, fire walls,nuclear reactors, munitions' boxes, chemical containers, batteries andautomobile exhaust systems.

[0011] Finally, these latent heat of fusion agents (PCMs) tend to burnat relatively high temperatures raising the overall heat content of thesystem. In addition, the reversibility of the phenomena virtuallyguarantees that these agents will also transfer heat into the heatsensitive devices once said devices are at a lower temperature than therespective temperatures of the agents. Consequently, not only do theseagents operate as heat absorbing agents, but in closed environments theyalso operate as heat transfer agents to cause the very damage to theheat sensitive devices that these agents were intended to protect in thefirst place. This they do by re-releasing the absorbed heat to the heatsensitive device, thereby increasing the time or duration that the heatsensitive device is exposed to a high heat environment.

[0012] It is, therefore, the object of the present invention to overcomethe disadvantages set forth above and, in particular, to provide fornonreversible heat absorbing applications.

[0013] It is a further object of the present invention to provideimproved coolant media for use in heat sensitive devices such asairplane and railroad crash recorders, missile electronics, munitionsboxes, clothing, firewalls, safe boxes, nuclear reactors, laser shields,thermal pulse shields, spacecraft devices, power supplies, datarecorders employed as aircraft and railroad components, combat devices,as well as in commercial uses such as oven sensors and the like.

[0014] It is another object of the present invention to provide heatabsorbing agents for use in heat sensitive devices, said heat absorbingagents being capable of absorbing heat at temperatures above 300° F.

[0015] It is another object of the present invention to provide heatabsorbing devices with mechanisms that utilize the chemical reactions oflatent heat of formation, decomposition or dehydration in suchmechanisms.

[0016] These objects as well as others will be found in detail in thedisclosure that follows below.

SUMMARY OF THE INVENTION

[0017] According to the present invention a heat absorbing device andmethod are provided comprising endothermic agents capable of absorbingheat for the cooling and maintenance of the temperature of heatsensitive devices at acceptable levels. Such endothermic agents comprisecertain acids and their salts, certain bases and their salts, certainhydrate salts and certain organic compounds. This means that they absorblarge quantities of heat to decompose or to dehydrate to either new andsimpler, chemically stable chemical compounds, or to their individualcomponent elements.

[0018] This ability to absorb heat and irreversibly decompose makes themideal for the thermal protection of heat sensitive devices inapplications where the integrity of the heat sensitive devices must bemaintained, under exposure to specified conditions of extreme high heat.

[0019] The shape, size and physical characteristics of the heatabsorbing devices and likewise the steps of the method are dictated bythe type of the heat sensitive device being protected, the heatsensitive device's spacial limitations, the heat sensitive device'sphysical environment and the heat generating conditions, to which theheat sensitive device will be subjected.

[0020] Similarly, the type and the amount of endotherms used in the heatabsorbing device and in the method are dictated by the heat sensitivityof the heat sensitive device; the maximum temperature at which the heatsensitive device can continue to be viable at; the extreme temperatures,to which the heat sensitive device will ultimately be subjected; thetime for which the heat sensitive device will be exposed to said extremeheat generating conditions; and the total thermal flux or thermal load,to which the heat sensitive device will be subjected.

[0021] Preferably, the endotherms can be boric acid; metal hydroxidesand their mixtures; carbonates and bicarbonates and their mixtures;salts of acetic acid, salts of formic acid, salts of boric acid, andtheir mixtures; paraldehyde, paraformaldehyde, and trioxane and theirmixtures; and hydrate salts and their mixtures. Further such endothermscan be supported within the device, via a(n) retaining matrix,packaging, encapsulation, microencapsulation, enclosure or structure toform a heat absorbing surface, device or structure.

[0022] The heat sensitive devices can be embedded within the endotherms;or they can be surrounded by the endotherms; or the endotherms can linethe walls (inner or outer) of the closed container within which the heatsensitive device is placed; or in the alternative, the endotherms can beadhered to a substrate (flexible or non-flexible) capable of beingadapted to the size and shape necessary for use with said heat sensitivedevices.

DETAILED DESCRIPTION

[0023] The features of the present invention will hereinafter bedescribed in detail.

[0024] The present invention utilizes non-recyclable, non-reversible,endothermic chemical reactions, which make use of the latent heat ofdecomposition and dehydration reactions to provide new, improved andparticularly, efficacious endothermic cooling systems.

[0025] What makes these non-recyclable, non-reversible, endothermicchemical reactions particularly appropriate for use in the inventiveheat absorbing device and method, is that these reactions havetemperatures of reaction that correspond to the temperature ranges takeninto consideration by the design of heat sensitive devices such asflight data recorders, electronics and related devices. Accordingly, thepresence of these reactions in the heat absorbing devices insures thatsaid heat absorbing devices act only as heat absorbers and not as heatgenerators; thereby being capable of maintaining the internaltemperature of the heat sensitive devices at a range between 100° C. and300° C., while said heat sensitive devices are being exposed to anexternal temperature range of 600° C. to 1100° C.

[0026] The compounds developed in the present invention provideendothermic chemical reactions, which are extremely stable in diverseenvironments, have long shelf life and high latent heats of reaction.Preferably, the compounds contemplated by the present invention include:boric acid and some borate salts; salts of acetic acid and formic acid;hydroxides of lithium, calcium, aluminum and sodium; carbonate salts ofmagnesium, lithium and silicon; paraldehyde, paraformaldehyde andtrioxane; and hydrated salts.

[0027] Specifically, the present invention makes a broad claim to adevice and method using endothermic agents which thermally decompose asfollows:

[0028] 1. Hydrated salts endothermically decompose to water and salt;

[0029] 2. Paraldehyde, paraformaldehyde and trioxane endothermicallydecompose to formaldehyde and thereafter to amorphous carbon, water,carbon dioxide and ethane;

[0030] 3. Low molecular weight acids endothermically decompose intowater and oxides; and

[0031] 4. Carbonate salts endothermically decompose into carbon dioxideand an oxide.

[0032] Generally, the inventive method involves taking an amount ofendotherm sufficient to effect the required heat absorption and eithercontacting said endotherm to the heat sensitive device, or supportingsaid endotherm between the heat sensitive device and the heat generatorso as to absorb the heat and prevent any increase in the temperature ofthe heat sensitive device. In either case, the amount of endotherm, thetype of endotherm, and the location of the endotherm can be determinedon the basis of the disclosure set forth below.

[0033] I. The following illustrates the endothermic reaction and heatabsorption of the aforementioned hydroxides when subjected to atemperature of reaction below 1100° C.

[0034] (a) LITHIUM HYDROXIDE: Lithium Hydroxide's use as an endotherm attemperatures below and up to 1100° C. is characterized by at least fourphases of heat absorption. FIG. 1 shows these four phases of heatabsorption, i.e. A, B, C and D, and the phenomena observed during suchphases. It is noted that the slopes of the graph are neither accuratenor precise but are only intended to be illustrative in nature.

[0035] Theoretically, the total amount of heat in calories absorbed byLiOH when exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B+C+D=Hrx

[0036] where

[0037] A=the amount of heat in calories absorbed by LiOH prior tomelting;

[0038] B=the amount of heat in calories absorbed during actual meltingphase of LiOH;

[0039] C=the amount of heat in calories absorbed by LiOH once melting iscomplete and it begins approaching its temperature of decomposition; and

[0040] D=the actual amount of heat of decomposition of LiOH in calories.

[0041] (i) Calculating the Hrx for LiOH:

[0042] The amount of heat in calories absorbed during Phase A as LiOH'stemperature begins to rise from room temperature i.e. 25° C. to itsMelting Point temperature of 462° C. is limited only by the specificheat of LiOH i.e. the amount of calories absorbed by 1 mole of LiOH tochange 1 degree Celsius. Consequently, one can theoretically calculatethe Phase A heat absorption by using LiOH's specific heat of 11.87cal/deg mol or 11.87/23.9484 (g/mol)=0.4956 cal/deg g (see CRC, HANDBOOKOF CHEMISTRY & PHYSICS, 63rd EDITION, P. D-74 (1982-1983)) as follows:(462° C.-25° C.)×0.4956 cal/deg g=217 cal/g. Thus, A=217 cal/g.

[0043] When the temperature of LiOH reaches its melting point i.e. 462°C., LiOH begins to melt. This begins Phase B. While the melting is goingon and until LiOH is completely liquid there is no change in temperature(ergo the flat line at Phase B). The amount of heat in calories absorbedduring such phase B at 462° C. is 103.3 cal/g. see CRC, HANDBOOK OFCHEMISTRY & PHYSICS 63RD EDITION, P. B-252 (1982-1983).

[0044] Once LiOH has completely melted, its temperature begins to rise.This begins phase C in FIG. 1. Just as in phase A, the amount of heatabsorbed during phase C is limited only by LiOH's specific heat of0.4956 cal/deg g. Thus, one can theoretically calculate the Phase C heatabsorption as follows: (1100° C.-462° C.)×0.4956 cal/deg g=316 cal/gi.e. C=316 cal/g.

[0045] When the temperature of the melted LiOH reaches its temperatureof decomposition, approximately 1100° C. LiOH begins to decompose, i.e.,

2LiOH decomposes to

Li₂O+2H₂O

[0046] This begins phase D. While the decomposition is going on anduntil LiOH is completely decomposed there is practically no change intemperature (ergo the flat line at Phase D). The amount of heat incalories absorbed during such phase D at approximately 1100° C. isapproximately 600 cal/g.

[0047] Therefore, based on the discussion above, the theoretical amountof heat absorbed by LiOH when used as an endotherm, is:

217 cal/g+103.3 cal/g+316 cal/g+600 cal/g=1236.3 cal/g.

[0048] It is seen from the foregoing that when LiOH decomposes at itsspecified temperature of reaction to form Lithium Oxide, it absorbs alarge quantity of latent heat of reaction. More importantly, however, ahigher amount of latent heat is absorbed by the melting of LiOH and itsheat capacity up to 1000° C. The above suggests that LiOH should be verygood at absorbing 686 cal/g for the decomposition, an extra 316 cal/gfor its heat capacity up to 1100° C., 103.3 cal/g for its melting at462° C. and 217 cal/g for its heat capacity to 462° C.

[0049] In fact, when LiOH was actually used as an endotherm in the heatabsorbing device of the present invention it was determined that itactually absorbed 1207 cal/g.

[0050] (b) SODIUM HYDROXIDE: Sodium Hydroxide's use as an endotherm attemperatures below and up to 1100° C. is similarly characterized by atleast four phases of heat absorption. FIG. 2 shows these four phases ofheat absorption, i.e. A, B, C and D, and the phenomena observed duringsuch phases. It is noted that the slopes of the graph are neitheraccurate nor precise but are only intended to be illustrative in nature.

[0051] Theoretically, the total amount of heat in calories absorbed byNaOH when exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B+C+D=Hrx

[0052] where

[0053] A=the amount of heat in calories absorbed by NaOH prior tomelting;

[0054] B=the amount of heat in calories absorbed during actual meltingphase of NaOH;

[0055] C=the amount of heat in calories absorbed by NaOH once melting iscomplete and it begins approaching its temperature of decomposition;and

[0056] D=the actual amount of heat of decomposition of NaOH in calories.

[0057] (i) Calculating Hrx for NaOH:

[0058] The amount of heat in calories absorbed during Phase A (FIG. 2)as NaOH's temperature begins to rise from room temperature i.e. 25° C.to its Melting Point temperature of 322° C. see CRC, HANDBOOK OFCHEMISTRY & PHYSICS, 63RD EDITION, P. B-253 (1982-1983) is limited onlyby the specific heat of NaOH, when NaOH is a solid i.e. the amount ofcalories absorbed by 1 mole of NaOH to change 1 degree Celsius.Consequently, one can theoretically calculate the Phase A heatabsorption by using NaOH's specific heat of 14.23 cal/deg mol or14.23/39.9972 (g/mol)=0.3558 cal/deg g see CRC, HANDBOOK OF CHEMISTRY &PHYSICS, 63rd EDITION. P. D-86 (1982-1983) as follows: (322° C.-25°C.)×0.3558 cal/deg g=105.6 cal/g. Thus, A=105.6 cal/g.

[0059] When the temperature of NaOH reaches its melting point i.e. 322°C., NaOH begins to melt. This begins Phase B (FIG. 2). While the meltingis going on and until NaOH is completely liquid there is no change intemperature (ergo the flat line at Phase B). The amount of heat incalories absorbed during such phase B at 322° C. is 50.0 cal/g. see CRC,HANDBOOK OF CHEMISTRY & PHYSICS 63RD EDITION, P. B-253 (1982-1983).

[0060] Once NaOH has completely melted, its temperature begins to rise.This begins phase C (FIG. 2). Just as in phase A, the amount of heatabsorbed during phase C is limited only by NaOH's specific heat of0.3558 cal/deg g. Thus, one can theoretically calculate the Phase C heatabsorption as follows: (1100° C.-322° C.)×0.3558 cal/deg g=276.8 cal/gi.e. C=276.8 cal/g.

[0061] When the temperature of the melted NaOH reaches its temperatureof decomposition, approximately 1100° C. NaOH begins to decompose, i.e.,

2NaOH decomposes to

Na₂O+2H₂O.

[0062] This begins phase D (FIG. 2). While the decomposition is going onand until NaOH is completely decomposed there is practically no changein temperature (ergo the flat line at Phase D). The amount of heat incalories absorbed during such phase D at approximately 1100° C. isapproximately 324 cal/g.

[0063] Therefore, based on the discussion above, the theoretical amountof heat absorbed by NaOH when used as an endotherm, is:

105.6 cal/g+50 cal/g+276.8 cal/g+324 cal/g=756.4 cal/g.

[0064] It is seen from the foregoing that when NaOH decomposes at itsspecified temperature of reaction to form Sodium Oxide, it absorbs alarge quantity of latent heat of reaction. More importantly, however, ahigher amount of latent heat is absorbed by the melting of NaOH and itsheat capacity up to 1000° C. The above suggests that NaOH should be verygood at absorbing 324 cal/g for the decomposition, an extra 276.8 cal/gfor its heat capacity up to 1100° C., 50.0 cal/g for its melting at 322°C. and 105.6 cal/g for its heat capacity to 322° C.

[0065] In fact, when NaOH was actually used as an endotherm in the heatabsorbing device, it was determined that it actually absorbed 585 cal/g.

[0066] (C) ALUMINUM HYDROXIDE: Aluminum Hydroxide's use as an endothermat temperatures below and up to 1100° C., on the other hand, ischaracterized by at least two phases of heat absorption. FIG. 3. showsthese two phases of heat absorption, i.e. A and B, and the phenomenaobserved during such phases. It is noted that the slopes of the graphare neither accurate nor precise but are only intended to beillustrative in nature.

[0067] Theoretically, the total amount of heat in calories absorbed byAl(OH)₃ when exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B=Hrx

[0068] where

[0069] A=the amount of heat in calories absorbed by Al(OH)₃ prior todecomposing; and

[0070] B=the amount of heat in calories absorbed by Al₂O₃ once thedecomposition is complete.

[0071] (i) Calculating Hrx for Al(OH)₃

[0072] The amount of heat in calories absorbed during Phase A (FIG. 3)as Al(OH)₃'s temperature begins to rise from room temperature i.e. 25°C. to its temperature of Decomposition of approximately 200° C. has beenfound to be approximately 324 cal/g. Aluminum Hydroxide decomposes asfollows:

2Al(OH)₃ decompose to

Al₂O₃+3H₂O

[0073] While the decomposition is going on and until Al(OH)₃ iscompletely decomposed there is practically no change in temperature(ergo the flat line at phase A). The amount of heat in calories absorbedduring such phase A is A=324 cal/g.

[0074] Once Al(OH)₃ is completely decomposed to Al₂O₃, Al₂O₃'stemperature begins to rise. This begins phase B in FIG. 8. The amount ofheat absorbed during phase B is limited only by Al₂O₃'s specific heat of0.1853 cal/deg g. see CRC, HANDBOOK OF CHEMISTRY & PHYSICS 63RD EDITION,P. D-53 (1982-1983).

[0075] Thus, one can theoretically calculate the Phase B heat absorptionas follows: (1100° C.-200° C.)×0.1853 cal/deg g=166.77 cal/g i.e.B=166.77 cal/g.

[0076] Therefore, based on the discussion above, the theoretical amountof heat absorbed by Al(OH)₃ when used as an endotherm, is:

324 cal/g+166.77 cal/g=490.77 cal/g.

[0077] It is seen from the foregoing that when Al(OH)₃ decomposes at itsspecified temperature of reaction to form Aluminum Oxide, it absorbs alarge quantity of latent heat of reaction. More importantly, however, ahigher amount of specific heat is absorbed due to the heat capacity ofAl₂O₃ up to 1100° C. The above suggests that Al(OH)₃ should be very goodat absorbing 324 cal/g for the decomposition, and an extra 166.77 cal/gfor Al₂O₃'s heat capacity up to 1100° C.

[0078] In fact, when Al(OH)₃ was actually used as an endotherm in a heatsink it was determined that it actually absorbed 510 cal/g.

[0079] II. The following illustrates the endothermic reaction and heatabsorption of the aforementioned carbonate salts, when they aresubjected to a temperature of reaction below 1100° C.

[0080] (a) CALCIUM CARBONATE: Calcium Carbonate's use as an endotherm attemperatures below and up to 1100° C., is characterized by at least twophases of heat absorption. FIG. 4 shows these two phases of heatabsorption, i.e. A and B, and the phenomena observed during such phases.It is noted that the slopes of the graph are neither accurate norprecise but are only intended to be illustrative in nature.

[0081] Theoretically, the total amount of heat in calories absorbed byCalcium Carbonate when exposed to temperatures below and up to 1100° C.can be mathematically represented by the following formula:

A+B=Hrx

[0082] where

[0083] A=the amount of heat in calories absorbed by CaCO₃ at itstemperature of decomposition;

[0084] B=the amount of heat in calories absorbed by CaO as itstemperature rises.

[0085] (i) Calculating Hrx for CaCO₃

[0086] The amount of heat in calories absorbed during Phase A (FIG. 4)by CaCO₃ at the temperature of Decomposition of approximately 825° C.has been found to be approximately 425.6 cal/g. see MERCK INDEX, TENTHEDITION, P. 228 (1983). Calcium Carbonate decomposes as follows:

CaCO₃ decomposes to

CaO+CO₂

[0087] While the decomposition is going on and until CaCO₃ is completelydecomposed there is practically no change in temperature (ergo the flatline at phase A). Thus, A=425.6 cal/g. It is noted that in the presenttheoretical calculations the amount of heat absorbed by CaCO₃ as itstemperature begins to rise from room temperature i.e. 25° C. to itsactual temperature of decomposition has been omitted, for simplicity'spurposes.

[0088] Once CaCO₃ is completely decomposed to CaO, now CaO's temperaturebegins to rise. This begins phase B in FIG. 4. The amount of heatabsorbed during phase B is limited only by CaO's specific heat of (19.57cal/deg mol)/(100.089 gr./mol)=0.1824 cal/deg g. see CRC, HANDBOOK OFCHEMISTRY & PHYSICS 63RD EDITION, P. D-59 (1982-1983).

[0089] Thus, one can theoretically calculate the Phase B heat absorptionas follows: (1100° C.-825° C.)×0.1824 cal/deg g=50.16 cal/g i.e. B=50.16cal/g.

[0090] Therefore, based on the discussion above, the theoretical amountof heat absorbed by CaCO₃ when used as an endotherm, is:

425.6 cal/g+50.16 cal/g=475.76 cal/g.

[0091] It is seen from the foregoing that when CaCO₃ decomposes at itsspecified temperature of reaction to form Calcium Oxide, it absorbs alarge quantity of latent heat of reaction. More importantly, however, ahigher amount of latent heat is absorbed by the heat capacity of CaO upto 1100° C. The above suggests that CaCO₃ should be very good atabsorbing 425.6 cal/g for the decomposition, and an extra 50.16 cal/gfor CaO's heat capacity up to 1100° C.

[0092] In fact, when CaCO₃ was actually used as an endotherm in a heatabsorbing device (heat shield) it was determined that it actuallyabsorbed 725.60 cal/g. This amount of heat is significantly higher thanthe amount of heat theoretically calculated above. This is logical whenone considers that (i) the theoretical calculations above did not takeinto consideration the heat absorbed by CaCO₃, during the time that itstemperature was rising from room temperature up to its temperature ofdecomposition (specific heat); and (ii) more likely than not, the CaCO₃was probably contaminated with small amounts of water, which has itsheat of vaporization; thereby adding to the total endothermic effectobserved during the testing of CaCO₃.

[0093] (b) SILICON CARBONATE (SiCO₃): On the basis of the discussion setforth above in connection with CaCO₃, it was theorized that SiliconCarbonate should exhibit the same type of endothermic absorptioneffects. In fact, when Silicon Carbonate was used as an endothermicmaterial it was found that:

[0094] (SiCO₃) decomposes to

SiO+CO₃ at 1100° C., and that it absorbs 380 cal/gm for decomposition.

[0095] (c) MAGNESIUM CARBONATE (MgCO₃): Similarly, when MagnesiumCarbonate was used as endothermic material it was found that thestarting endothermic material is composed of Magnesium Carbonate(MgCO₃), Magnesium Hydroxide (Mg(OH)₂) and Water (H₂O). i.e., n MgCO₃:nMg(OH):n H₂O; and that

[0096] n MgCO₃:n Mg(OH)₂:n H₂O decomposes to

nMgO+nCO₂ and nH₂O at 700° C. The amount of heat absorbed during suchdecomposition was 285 cal/gm.

[0097] III. Other reactions which can provide endothermic cooling ofheat sensitive devices, other surfaces and structures via heatabsorption i.e. endothermic mechanisms similar to those described aboveare as follows:

[0098] (a) SODIUM BICARBONATE: The Thermal Decomposition of sodiumbicarbonate absorbs in excess of 350 cal/gm between 120° C. and 310° C.i.e.

2 NaHCO₃

Na₂CO₃+H₂O+CO₂

T=270° C.

Δ H_(r)=363 cal/g

[0099] (b) SODIUM BICARBONATE: The Thermal Decomposition of sodiumbicarbonate absorbs in excess of 320 cal/gm between 200° C. and 375° C.i.e.

[0100] (c) BORIC ACID: In particular, it has been found that boric acidabsorbs large amounts of heat when decomposing, because boric aciddecomposes in stages over a range of temperatures to produce boron oxideand water while absorbing nearly 400 cal/g. Borate salts act similarlyfor effective heat absorption results.

[0101] Specifically, the Thermal Decomposition of Boric Acid absorbs inexcess of 400 cal/gm between 120° C. and 350° C. i.e.

[0102] IV. The following illustrate the endothermic reaction and heatabsorption of hydrated salts for the cooling of heat sensitive devices,other surfaces and structures via heat absorption mechanisms similar tothose described above when subjected to a temperature reaction below1100° C. Specifically the following hydrate salts provide effectiveendothermic cooling from 60° C. through 200° C.:

[0103] (a) HYDRATED SALT OF LITHIUM CHLORIDE: This reaction will provideendothermic cooling of electronic devices and other surfaces andstructures by the thermal decomposition of lithium chloride trihydrateabsorbing in excess of 440 cal/g between 90° C. and 150° C. i.e.

[0104] (b) HYDRATED SALT OF MAGNESIUM CHLORIDE:

[0105] (c) HYDRATED SALT OF MAGNESIUM SULFATE: This reaction willprovide endothermic cooling of heat sensitive devices and other surfacesand structures by the thermal decomposition of magnesium sulfateheptahydrate absorbing in excess of 350 cal/g between 120° C. and 250°C. i.e.

[0106] (d) HYDRATED SALT OF SODIUM SULFATE:

[0107] (e) HYDRATED SALT OF ALUMINUM OXIDE:

[0108] (f) HYDRATED SALT OF ALUMINUM SULFATE:

[0109] (g) HYDRATED SALT OF ALUMINUM FLUORIDE:

[0110] (h) HYDRATED SALT OF ALUMINUM NITRATE:

[0111] An additional endothermic effect may be obtained by the furtherdecomposition of Al₂(NO₃)₃.

[0112] (i) HYDRATED SALT OF LITHIUM NITRATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of lithium nitrate trihydrateabsorbing in excess of 320 cal/g between 50° C. and 120° C. i.e.

[0113] (j) HYDRATED SALT OF SODIUM CARBONATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium carbonate decahydrateabsorbing in excess of 320 cal/g between 20° C. and 80° C. i.e.

[0114] (k) HYDRATED SALT OF SODIUM BORATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium borate decahydrateabsorbing in excess of 350 cal/g between 200° C. and 375° C. i.e.

[0115] (l) HYDRATED SALT OF BERYLLIUM SULFATE: This reaction willprovide endothermic cooling of heat sensitive devices and other surfacesand structures by the thermal decomposition of beryllium sulfatequatrohydrate absorbing in excess of 300 cal/g between 90° C. and 450°C. i.e.

[0116] (m) HYDRATED SALT OF SODIUM PHOSPHATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium phosphatedodecahydrate absorbing in excess of 300 cal/g between 80° C. and 150°C. i.e.

[0117] (n) HYDRATED SALT OF CALCIUM CHLORIDE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of calcium chloride hexahydrateabsorbing in excess of 300 cal/g between 220° C. and 350° C. i.e.

[0118] (o) HYDRATED SALT OF ZINC SULFATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of zinc sulfate heptahydrateabsorbing in excess of 300 cal/g between 220° C. and 350° C. i.e.

[0119] IV. Other endothermic reactions that have been found suitable foruse in the present inventive heat absorbing devices on the basis of theprinciples set forth above, are the decomposition of paraldehyde,paraformaldehyde and trioxane which, likewise, result in relativelylarge scale endothermies.

[0120] Several of the reaction products of the combination of theaforementioned materials such as lithium acetate, lithium formate andtheir hydrates may also be used. The graphs 5 and 6 show the naturaldelay in temperature rise for lithium formate and lithium acetatethermal decomposition reactions.

[0121] It has also been found that the salts of acetic acid and formicacid and their hydrates result in large scale endothermic reactions andabsorptions of large quantities of heat. Accordingly, these formic andacetic acid salts are also suitable for use in the present inventiveheat absorbing devices.

[0122] IV. The compounds of the present invention may be supportedwithin the inventive heat absorbing device via composite fabric carriersor matrices of the type discussed in Applicant's aforementionedapplication and in the prior noted patents, to form an endothermicstructure. Additionally, the compounds can be supported up against theheat sensitive device as an endothermic structure via a retainingmatrix, packaging, encapsulation, microencapsulation, enclosure, orstructure; or by being suspended in other media; or they themselves maybe used in bulk to form the endothermic structure. Irrespective of thesupport or whether they themselves form the endothermic structure, saidendothermic structure can be measured, cut and fit to form (i) a heatabsorbing surface up against the heat sensitive device; (ii) anenclosure or container, within which the heat sensitive device can beplaced; or (iii) a thermal barrier structure or shield between a heatgenerator and the heat sensitive device. If the compounds have not beenformed into an endothermic structure, supported or otherwise, they couldbe simply deposited around the heat sensitive device. Anotherembodiment, the retaining structure can be made of a low thermalconductivity material (or a thermal insulator) such as a plastic orpolyamide.

[0123] Thus, in one embodiment of a heat absorbing device designed toprotect a heat sensitive device from external heat, the endothermiccompounds are enclosed within the walls of an enclosure. As used hereinthe term enclosure includes containers or box-like structures of anysize or shape. In another embodiment of a similar heat absorbing device,the compounds line the inner surface of the walls of the enclosure. In athird embodiment of said heat absorbing device, the endothermiccompounds line the outer surface of the walls of the enclosure. In yetanother embodiment of said device, the endothermic compounds are packedaround the heat sensitive device, surrounded with a retaining structureso that it stays packed around the heat sensitive device, and thewrapped device is then placed in the enclosure. The retaining structurecan, if desired, be a thermally conductive structure.

[0124] On the other hand, in an embodiment of a heat sensitive devicedesigned to protect a heat sensitive device from its own self-generatedinternal heat, the endothermic compounds are poured into a container orsupported by a structure and the heat sensitive device is embeddedtherein. Of course, if the heat sensitive device is embedded within theendothermic compound, it is imperative to choose an endothermic compoundwhose temperature of reaction is suitable for the particularapplication, and whose decomposition and/or dehydration products willnot affect the heat sensitive devices.

[0125] It is clear from the above that the position or location of theendothermic compounds is not fixed relative to the heat sensativedevice, any outer structure supportive or its insulation. Rather suchposition or location is dependent on the application and the heatsensitive device's design specifications and heat tolerance. Similarly,the enclosure's shape is not limited. In fact, the shape and dimensionsthereof may or may not be limited by the application and the heatsensitive device's design specifications.

[0126] When the heat absorbing device comprises endothermic compoundswithin or lining its walls (either outer or inner), as is in the case ofa heat absorbing device designed to protect from external heat (seediscussion above), the heat sensitive device can be placed within theenclosure either snugly, with no space between it and the walls of saidenclosure; or loosely so that there is a defined space or a gap betweenit and the enclosure's walls.

[0127] If the heat sensitive device is placed so that it fits snuglywithin the enclosure, then the enclosure will be sealed to protect theheat sensitive device from the external high heat conditions, and theentire package can be further wrapped in insulation to further protectthe heat sensitive device from the outside high temperatures.

[0128] On the other hand, if the heat sensitive device is placed so thatit fits to form a gap between it and the heat absorbing enclosure, alayer of insulation can be placed in the gap between the heat sensitivedevice and the enclosure's walls. This adds another layer of protectionagainst the outside heat. The enclosure is then sealed and if desiredcan be further wrapped in another layer of insulation to further protectthe heat sensitive device from the outside high heat.

[0129] In a preferred embodiment, however, of the heat absorbing devicedesigned to protect from external heat, said device is placed adjacenttot he heat sensitive device; thereafter insulation is wrapped orsurrounded about the device and heat absorber and the entire package maybe placed in a housing.

[0130] In one application using the present invention, a flight datarecorder is provided with a heat absorbing shield. The shield is inessence a single, flat, rectangular block very similar to a small brick.It is sized in length, height and width so that it could lie right upagainst and contact the surface of the flight data recorder circuitboard, which requires protection. The shield consists of cakes of boricacid held together and retained with metal or plastic. The boric acidwafers are formed by compression into rectangular cakes, which fitneatly into the shield's metal or plastic retainer.

[0131] The boric acid shield is then laid up against the circuit boardof the memory control system of the flight data recorder. Theaccompanying graphs 7 and 8 show the natural rise in temperature of aconventional beryllium or wax heat sink when used with the flight datarecorder, as compared to the same flight recorder's thermal performancewith a boric acid heat absorbing shield formed in accordance with thepresent invention described above.

[0132] In other applications of the invention, the flight recorder isplaced within boric acid box-like structures; each differing only in thelocation of the boric acid, as described above. The structures are thensealed to protect the flight data recorder from the external high heatconditions and subjected to thermal loads in excess of fifty thousandwatts per one hour (1 watt=3600 joules; 1 cal=4,1850 joules), which isthe present government standard for testing flight recorders.

[0133] Again it was found that the flight recorder's thermal performanceafter it was sealed within any of the boric acid structures taughtabove, was substantially better than the thermal performance of the sameflight recorder applying a conventional beryllium or wax heat sinkthermally protective structure.

[0134] Graph 9 shows the use of a hydrated salt i.e. MgSO₄.7H₂O inaccordance with the teachings set forth above, and how such use resultedin a strong cooling effect as applied to the flight recorder of Graph 7.

[0135] V. The ultimate shape, size and physical characteristics of theheat absorbing device, as well as the type and amount of endothermicmaterial used, are dictated by many factors. These factors include thetype of heat sensitive device being protected; the time period for whichthe heat sensitive device will be exposed to high heat; the temperaturesto which the heat sensitive device will be ultimately exposed; and thethermal sensitivity of the heat sensitive device.

[0136] Thus, for example, if a flight recorder contains electronics madeof materials that are particularly sensitive to high heat, one mightchoose to enclose the electronics completely within an endothermic andinsulated enclosure, as described above. On the other hand, if theelectronics are less sensitive to high heat, one might opt for the useof a single thin endothermic compound “shield”, as a thermal controlsystem.

[0137] Similarly, if the flight recorder will be exposed to very hightemperatures, as for example 600° C. through 1100° C. for more than justa few minutes, one would not only choose to enclose the flight recorderwithin an endothermic compound “box”, but one would use an endothermfrom those described above that decompose within that temperature rangei.e. Lithium Hydroxide, Sodium Hydroxide or Aluminum Hydroxide; or usemore insulation within the “box” and pick any of the endothermiccompounds disclosed above; or use multiple layers or mixtures ofdifferent endotherms, set to react at different temperatures. Moreimportantly, however, one would have to calculate, on the basis of theformulas set forth above, the amount of the endotherm(s) that wouldactually have to be contained within the “box” so that it couldefficiently and completely absorb the damaging thermal load, to whichthe flight recorder will be subjected.

[0138] On the other hand, if the flight recorder is going to be exposedto temperatures between 120° C. and 350° C., one can choose to encloseit within a boric acid “box.” The amount of boric acid within the wallsof the “box” or the amount of boric acid surrounding the flight recordereither through its being poured onto the flight recorder, or through itsbeing lined onto the inner surface of the “box” can be calculated on thebasis of Δ H_(r)=(53,600 Kcal/2 mol) (2(62) g/2 mol≧432 cal/g.Specifically, one would have to calculate the amount of heat that theflight recorder would be exposed to over time. The method of saidcalculation is well known in the art. Thus, if the amount of damagingheat to which the flight recorder will be exposed over ten minutes willbe 432000 cal, then the amount of boric acid surrounding the flightrecorder in the box should be equal to or more than one thousand grams.

[0139] VI. Aluminum Hydroxide (Al(OH)₃) devices work best as a hightemperature endothermic temperature control devices. When aluminumhydroxide decomposes, it leaves behind a strong thermal insulation layerof aluminum oxide (see above), which further abates a temperature risethrough the decomposition products which is deposited within the heatabsorbing device.

[0140] Other applications of the present invention presented, by way ofexample and not as a limitation include: temperature control coatings,wraps and liners, as well as thermal protection for metal and plasticstructures; cooling for electronics, oven sensors, missile skins,exhaust pipes, thermal protection in race cars, fire walls, emergencycooling for nuclear reactors, guns, munitions boxes, batteries andrelated equipment; and in structures designed to shield life fromthermal harm.

[0141] Unlike salt hydrates discussed above, hydroxides or carbonatesmay be stored almost indefinitely provided they are not exposed totemperatures at or above the temperature of reaction. When exposed toreduced pressure and some heat, hydrates tend to lose water, making themless likely to be fully effective as cooling agents in some aircraftapplications, unless properly hermetically sealed, with allowance topermit venting of water vapor at the temperature of reaction.

[0142] All of the endothermic compounds listed and discussed above arecommercially available and inexpensive. They may be easily incorporatedin and integrated in CFEMs, metal mesh matrices, silicon or carbon fiberor microencapsulated in porous silicate, porous carbon bodies, orsuspended in plastics such as fluoroelastomers, teflon, metals or othermaterials. The agents may be shaped in the form of enclosures, chips, orcakes which can be incorporated in shaped bodies, and thus, can beformed in shape and dimension as required. In some applications theagents may be formed into gels and pastes.

[0143] The special compounds of the present invention provideunforeseen, critical benefits in that they readily absorb massivequantities of heat, in a unidirectional reaction. And that once theyabsorb it, they do not release it, they do not reverse, and thereforecannot act as heat generating compounds. Thus, protection for heatsensitive devices is significant and substantial within a closedenvironment.

[0144] Furthermore, all of these compounds produce environmentallyharmless vapor products during decomposition and even at elevatedtemperatures. In addition, since these compounds are per se generallynon-toxic (as compared to Beryllium, a material used in prior art heatsinks and which is extremely toxic) they are easier and less expensiveto use in the manufacturing process of the heat absorbing devices.

[0145] Various modifications and changes have been disclosed herein, andothers will be apparent to those skilled in this art. Therefore, it isto be understood that the present disclosure is by way of illustrationand not limitation of the present invention.

What is claimed is:
 1. An article of manufacture for the prevention ofthe increase of temperature in heat sensitive devices through theabsorption of heat during heat generating conditions comprising analdehyde in an amount sufficient to effect the required heat absorption;and means for supporting said aldehyde, the physical characteristics ofsaid means for supporting said aldehyde being defined by the heatabsorbing application.
 2. The article of manufacture according to claim1, wherein the aldehyde is selected from the group consisting offormaldehyde (methanal), acetaldehyde (ethanol), propionaldehyde(propanol), n-butyraldehyde (butanol), benzaldehyde,p-Nitrobenzaldehyde, p-tolualdehyde, salicylaldehyde(ortho-hydroxybenzaldehyde), phenyacetaldehyde (phenylethanol),alpha-methlvaleraldehyde (z-methylpentanol), 4-methylpentanol),paraformaldehyde, trioxane, dioxane, paraldehyde and the mixturesthereof.
 3. The article of manufacture according to claim 1, wherein themeans for supporting said aldehyde further comprises a retaining matrix,packaging, encapsulation, microencapsulation, enclosure or structure toform a heat absorbing surface, device or structure.
 4. The article ofmanufacture according to claim 1, wherein the heat sensitive device isembedded within the aldehyde.
 5. The article of manufacture according toclaim 1, wherein the heat sensitive device is surrounded by thealdehyde.
 6. The article of manufacture according to claim 1, whereinthe means for supporting said aldehyde is a closed container, withinwhich said aldehyde is located.
 7. The article of manufacture accordingto claim 6, wherein said aldehyde lines the inner wall of the closedcontainer.
 8. The article of manufacture according to claim 7, whereinsaid heat sensitive device is located within and spaced from saidaldehyde.
 9. The article of manufacture according to claim 1, whereinsaid aldehyde is adhered to a flexible substrate, said substrate beingadaptable to the size and shape of said heat sensitive device.
 10. Thearticle of manufacture according to claim 1, wherein the means forsupporting said aldehyde is the aldehyde itself.